1. Field of the Invention
The present invention relates to a method and apparatus for improving interaction between a Scheduling Request procedure and a Random Access procedure, and more particularly, to a method and apparatus for improving interaction between a Scheduling Request procedure and a Random Access procedure in a user equipment (UE) of a wireless communication system, so as to avoid uplink transmission error or failure of the Random Access procedure when the Random Access procedure is triggered by the Scheduling Request procedure.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
In LTE system, the network, such as an evolved Node B (eNB), performs radio resource allocation to provide user equipments (UEs) with resources for uplink or downlink data transfer. There are two kinds of resource allocations: dynamic resource allocation and pre-configured resource allocation. For the pre-configured resource allocation, the network allocates resource to the UEs by Radio Resource Control (RRC) signaling, and allows the UEs periodically transmitting a certain amount of data, for example, voice data. That means, at periodic time intervals, the UEs can utilize the pre-configured radio resources for data transmission or reception, to achieve data exchange with the network. On the other hand, for the dynamic resource allocation, the network dynamically allocates radio resources to the UEs depending on UE number of the cell area, traffic volume and quality of service (QoS) requirements of each UE, and the UE has to monitor a physical downlink control channel (PDCCH) to find possible allocation of dynamic resources for both downlink and uplink transmission.
Besides, for the dynamic resource allocation, when the UE has new uplink data to transmit and there is no Uplink Shared Channel (UL-SCH) resource available, the UE shall trigger a Scheduling Request (SR) procedure to request the network to allocate uplink transmission resources. In such a situation, if the UE has configured Physical Uplink Control Channel (PUCCH) resources, the SR procedure is performed via PUCCH signaling. Otherwise, such as the UE has no configured PUCCH resources or the configured PUCCH resources are invalid, for example, the SR procedure is then performed via a Random Access Procedure. Since the PUCCH resources are dedicated transmission resources, the SR message transmitted on PUCCH is referred to as a Dedicated Scheduling Request (D-SR) message, while the SR message transmitted via the Random Access procedure is referred to as an Random Access Scheduling Request (RA-SR) message.
According to current specifications, if the UE has a configured PUCCH resource after the SR procedure is triggered, the UE shall periodically transmit a D-SR message on PUCCH until an uplink transmission resource for a new transmission is received or the number of D-SR transmissions reaches to a pre-defined parameter DSR_TRANS_MAX. When the number of D-SR transmissions reaches to the pre-defined parameter DSR_TRANS_MAX, it indicates uplink transmission of the UE may have some problem, such as the PUCCH resources become invalid or the UE loses synchronization on uplink timing, and thus the D-SR messages sent by the UE cannot be successfully received by the network. In this case, the UE shall stop the D-SR transmission, release all configured PUCCH resources, and trigger a Random Access procedure to transmit the SR message instead. Note that the pre-defined parameter DSR_TRANS_MAX is configured by RRC signaling.
However, if the UE already has pre-configured transmission resources, such as Semi-Persistent Scheduling (SPS) resources, when the number of D-SR transmissions reaches to the pre-defined parameter DSR_TRANS_MAX, since some problem may already occur on uplink transmission of the UE, continuing using the pre-configured resources to perform uplink transmission may cause transmission failure or interference to other UE's transmission. Moreover, when the UE switches to use the Random Access procedure to transmit the SR message, the pre-configured resources may collide with UL-SCH resources carried by Message 2 (Msg 2) of the Random Access procedure. As a result, Message 3 (Msg 3) of the RA procedure may misuse the pre-configured resource for transmission, and cause failure of the Random Access procedure which makes the UE unable to obtain the uplink transmission resources.